1. Field of the Invention
The present invention relates to a time-division multiplexing transmission system, and more particularly to a time-division multiplexing transmission system for performing channel identification in the case where each of a plurality of signals including at least one frame structure signal having frame structure is multiplexed as one channel and transmitted in a time-division manner.
2. Description of the Prior Art
A conventional time-division multiplexing transmission system is disclosed in Japanese Patent Application Laid-Open No. 2-253735. A description will be made of this conventional system in reference to FIG. 15.
In the figure, in the conventional system, a frame synchronization signal is first added to a specific channel signal by a frame synchronization signal addition circuit 111. Then, signal addition circuits 112 to 114 add signals differing from the frame synchronization signal to the other channels instead of adding respective frame synchronization signals. Next, these channel signals are multiplexed and transmitted on a transmission path by a multiplexer 121.
A demultiplexer 131 demultiplexes the output signal from the multiplexer into four individual channel signals. Frame synchronization is performed on the four channels by frame synchronization signal detection circuits 141 to 144. At this time, it can be judged that the channel in which frame synchronization has been established is the above-mentioned specific channel. A channel switching circuit 151 performs a switch of the channels on the basis of the outputs of the frame synchronization signal addition circuits 141 to 144.
In the above-mentioned conventional time-division multiplexing transmission system, at the transmitter side there is a need to add a new frame synchronization signal to a specific channel and add signals differing from the frame synchronization signal to the other channels. For this reason, the channels require signal addition circuits respectively, and consequently, there is a disadvantage that the entire size of the system is increased.
Also, this conventional transmission system has another disadvantage that it requires circuitry which operates at a higher transmission rate, because the above-mentioned signals are added.
The prevent invention has been made in order to solve the above-mentioned disadvantages of the prior art, and the objective is to provide to a time-division multiplexing transmission system which is structurally simple and where there is no increase in the size.
To achieve this end, there is provided a time-division multiplexing transmission system for multiplexing and transmitting a plurality of channels of signals which include at least one frame structure signal having frame structure in a time-division manner, the time-division multiplexing transmission system comprising: a transmitter having inversion means for inverting at least some of synchronization patterns in the frame structure signal and time-division multiplexing means for multiplexing and transmitting a plurality of channels of signals which include a signal having the inverted synchronization patterns in a time-division manner; and a receiver having demultiplexing means for demultiplexing the time-division multiplexed channels into individual channels, also having frame synchronization means for performing frame synchronization on the basis of the channel having the inverted frame synchronization patterns among the demultiplexed channels, and further having channel identification means for using the frame synchronized channel as a reference and recognizing the remaining channels.
In the transmitter, at least some of synchronization patterns in a signal having frame structure are inverted, and a plurality of channels of signals which include a signal having the inverted synchronization patterns are multiplexed and transmitted in a time-division manner. In the receiver, the time-division multiplexed channels are demultiplexed into individual channels. Then, frame synchronization is performed on the basis of the channel having the inverted synchronization patterns among the demultiplexed channels. With the frame synchronized channel as a reference, the remaining channels are identified. With this constitution, the system becomes structurally simple and there is no possibility that the size of the system will be increased.